Yeah they are tapered. While putting it together I put a good amount of gun oil on each side, locked it up in a vice and torqued the crap out of it with a big pair of pliers. Its probably not ever getting any tighter or ever coming apart.Are the nipples tapered? If so, cutting the nipples down wont give you much. Tapered nipples can only be tightened down so far and cutting threads off would give your fittings less to hold on to. I used to be a pipe fitter and this was my experience.
Best advice I'd say is to get 2 pipe wrenches and tighten down with as much muscle as you can (if you haven't already done so). Try wrapping the piece in a rag to prevent teeth marks from the wrenches.
You think Jedi have these under there sinks?